Relative rate constants for the reactions of OH radicals with H2, CH4, CO, NO and HONO at atmospheric pressure and 296 K

Abstract

The photolysis of gaseous HONO has been studied in the presence of added H₂, CH₄, CO and NO at room temperature and atmospheric pressure. From the effects of these gases on the formation of NO and NO₂ in the photolysis, the rate constants for the reactions of hydroxyl radicals with these added gases have been determined relative to the reaction OH + HONO = H₂O + NO₂. Using a consensus mean value of 7.0 × 10^–15 cm³ molecule^–1 s^–1 at 298 K for the reaction OH + H₂= H₂O + H the following rate constants in cm³ molecule^–1 s^–1 units are derived. OH + CH₄= H₂O + CH₃k=(7.6 ± 0.5)× 10^–15, OH + CO = CO₂+ H k=(2.7 ± 0.2)× 10^–13, OH + NO(+M)= H₂O + NO₂k=(1.17 ± 0.17)× 10^–11(M = 1 atm. N₂+ O₂), OH + HONO = H₂O + NO₂k(6.6 ± 0.3)× 10^–12. These rate constants are consistent with other literature values obtained by a number of techniques, with the exception of the OH + CO reaction for which direct determinations made at lower total pressures give a value of close to 1.5 × 10^–13 cm³ molecule^–1 s^–1. It is suggested that this reaction may be subject to a pressure effect.